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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

D.M.S. S. V.H COLLEGE OF ENGINEERING (Affiliated to Acharya Nagarjuna University)

(Approved by AICTE) MACHILIPATNAM - 521 002 (A.P) 2007 – 2008

ROUTE FINDING USING GLOBAL POSITIONING SYSTEM A PORJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DEGREE OF BACHELOR OF TECHNOLOGY IN ELECTRONICS AND COMMUNICATION ENGINEERING Submitted by PADMA PRIYA. A ABZAL BASHA. SK SRINIVAS NAIDU. N DEVILAL BAHADUR. T Under The Esteemed Guidance of Mr. P. Sekhar M. Tech Lecturer

L5EC603 Y4EC602 Y4EC663 Y2EC650

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

D.M.S. S. V.H COLLEGE OF ENGINEERING (Affiliated to Acharya Nagarjuna University)

(Approved by AICTE) MACHILIPATNAM - 521 002 (A.P) 2007 – 2008

ROUTE FINDING USING GLOBAL POSITIONING SYSTEM A P ROJE CT REP OR T SUB MITTE D IN PARTI AL F ULFILL MENT O F THE REQ UI RE MENTS FO R THE A WA RD OF DE GREE OF

BACHELOR OF TECHNOLOGY IN ELECTRONICS AND COMMUNICATION ENGINEERING Submitted by PADMA PRIYA. A ABZAL BASHA. SK SRINIVAS NAIDU. N DEVILAL BAHADUR. T Under The Esteemed Guidance of

L5EC603 Y4EC602 Y4EC663 Y2EC650

Mr. P. Sekhar M. Tech DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

D.M.S. S. V.H COLLEGE OF ENGINEERING (Affiliated to Acharya Nagarjuna University)

(Approved by AICTE) MACHILIPATNAM - 521 002 (A.P) 2007 – 2008

CERTIFICATE This is to certify that “ROUTE FINDING USING GLOBAL POSITIONING SYSTEM” is bonafide project work done by PADMA PRIYA. A ABZAL BASHA. SK SRINIVAS NAIDU. N DEVILAL BAHADUR. T

L5EC603 Y4EC602 Y4EC663 Y2EC650

Submitted in partial fulfillment of the requirement of the award of the degree of Bachelor of technology In ELECTRONICS & COMMUNICATION ENGINEERING discipline During Academic year 2007 – 20008. Head of the Department Sri. R. S.SASTRY Professor

Project Guide MR. P. SEKHAR, M.Tech Lecturer

External Examiner

ROUTE FINDING USING GLOBAL POSITIONING SYSTEM ABSTRACT : Global Positioning System is an earth-orbiting-satellite based system that provides signals available anywhere on or above the earth, twenty-four hours a day, which can be used to determine precise time and the position of a GPS receiver in three dimensions. Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers. Time and frequency dissemination, based on the precise clocks on board the Satellite Vehicles (SV) and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers. Latitude and longitude are usually provided in the geodetic datum on which GPS is based (WGS-84).  Receiver position is computed from the SV positions, the measured pseudo-ranges, and a receiver position estimate.  Four satellites allow computation of three position dimensions and time.  Three satellites could be used determine three position dimensions with a perfect receiver clock.  In practice this is rarely possible and three SVs are used to compute a two-dimensional, horizontal fix (in latitude and longitude) given an assumed height.  Five or more satellites can provide position, time and redundancy.  Twelve channel receivers allow continuous tracking of all available satellites, including tracking of satellites with weak or occasionally obstructed signals. The parameters like latitude, longitude, altitude and speed are received from GPS via RS232 these parameters are compare with the predefine wave points and when status of success is displayed on the LCD along with these instant latitude, longitude, altitude and speed parameters are also displayed on the LCD.

To achieve this we are going to use one GPS module and one GSM module, which are connected to a micro controller unit. Whenever the user sends an SMS to the GSM modem, micro controller unit will get the appropriate request by sending standard AT commands, and sends request to GPS module from the micro controller in the form of NMEA standard command sentences, to get the vehicle longitude and latitude. After that by processing the received data in micro controller, the reverse SMS with position will send to the user’s number from GSM modem. The GPS module in this system will communicate with the satellite and receives its current position (vehicle position). If any theft occurs we can lock the doors remotely again by sending SMS. Software: IDE:

Embedded C and Assembly.

KEIL Uvision2. Hardware: 1. GSM modem 2. GPS receiver. 3. ATMEL 89s52 micro controller 4. Max 232 IC. 5. Db 9 connectors 6.11.0592MHZ crystals 7. Resistors and capacitors 8. IC bases and connectors 9. Relay drivers and relays. 10.8250 USART

CHAPTER 1

INTRODUCTION TO GPS

Using the Global Positioning System GPS, a process used to establish a position at any point on the globe) the following two values can be determine any where on Earth (Figure1): 1. One’s exact location (longitude, latitude and height co-ordinates) accurate to within a range of 20mto approx.1mm. 2. The precise time (Universal Time Coordinated, UTC) accurate to within a range of 60ns to approx. 5ns. Speed and direction of travel (course) can be derived from these co-ordinates as well as the time. The coordinates and time values are determined by 28 satellites orbiting the Earth.

The basic function of GPS

GPS receivers are used for positioning, locating, navigating, surveying and determining the time and are employed both by private individuals (e.g. for leisure activities, such as trekking, balloon flights and cross-country skiing etc.) and companies (surveying, determining time, navigation, vehicle monitoring etc.) GPS (the full description is: NAVigation System with Timing And Ranging Global Positioning System, NAVSTAR-GPS) was developed by the U.S. Department of defense (DoD) and can be used both by civilians and military personnel. The civil signal SPS (Standard Positioning Service) can be used freely by the general public, whilst the military signal PPS (Precise Positioning Service) can only is used by authorized government agencies. The first satellite was placed in orbit on 22nd February 1978, and there are currently 28 operational satellites orbiting the earth at a height of 20, 180 km on 6 different orbital planes. Their orbits are

inclined at 550 to the equator, ensuring that a least 4 satellites are in radio communication with any point on the planet. Each satellite orbits the Earth in approximately 12 hours and has four atomic clocks on board. During the development of the GPS system, particular emphasis was placed on the following three aspects: 1. It had to provide users with the capability if determining position, speed and time whether in motion or rest. 2. It had to have a continuous, global, 3-dimensional positioning with a high degree offer of accuracy, irrespective of weather. 3. It had to offer potential for civilian use.

Determining the distance of a lightning flash

Distance = transit time • the speed of sound The GPS system functions according to exactly the same principle In order to calculate one’s exact position; all that needs to be measured is the signal transit time between the point of observation and four different satellites whose positions are known. Generating GPS signal transit time 28 satellites inclined at 55° to the equator orbit the Earth every 11 hours and 58 minutes at a height of 20,180 km on 6 different orbital planes. (Figure). Each one of these satellites has up to four atomic clocks on board. Atomic clocks are currently the most precise instruments known, losing a maximum of one second every 30,000 to 1,000,000 years. In order to make them even more accurate, they are regularly adjusted or synchronized from various

control points on Earth. Each satellite transmits its exact position and it’s precise on board clock time to Earth at a frequency of 1575.42MHz.These signals are transmitted at the speed of light (300,000 km/s) and therefore require approx. 67.3ms to reach a position on the Earth’s surface located directly below the satellite. The signals require a further 3.33 us for each excess kilometer of travel. If you wish to establish your position on land (or at sea or in the air), all you require is an accurate clock. By comparing the arrival time of the satellite signal with the on board moment the signal was emitted, it is possible to determine the transit time of that signal (Figure)

GPS satellites orbit the Earth on 6 orbital planes

Determining a position on a plane

Figure 5: The position of the receiver at the intersection of the two circles

Figure 6: The position is determined at the point where all three spheres intersect

The effect and correction of time error

Determining a position in 3-D space

figure 7: Four satellites are required to determine a position in 3-D space.

3.1 Description of the entire system

Figure 8: The three GPS segments

Space segment Satellite movement

Figure 9: Position of the 28 GPS satellites at 12.00 hrs UTC on 14th April 2001

The GPS satellites Construction of a satellite

Figure 11: A GPS satellite 3.2.2.2 The communication link budget analysis

Generating the satellite signal Simplified block diagram

Figure 13: Simplified satellite block diagram

Figure 14: Data structure of a GPS satellite

Detailed block system

Comparison between ephemeris and almanac data

Table 2: Comparison between ephemeris and almanac data

Figure 19: Ephemeris terms

Calculating a position

Figure 20: Four satellite signals must be received

Figure 21: Three dimensional co-ordinate system

5.2.2 Linearisation of the equation

Figure 22: Conversion of the Taylor series

Figure 23: Estimating a position

Solving the equation

Summary

Error consideration and satellite signal Error consideration

Table 4: Cause of errors

5.2.5.2 DOP (dilution of precision)

Figure 24: Satellite geometry and PDOP

Figure 25: GDOP values and the number of satellites expressed as a time function

Figure 26:

Effect of satellite constellations on the DOP value

DIFFERENTIAL-GPS (DGPS): Introduction

DGPS based on the measurement of signal transit time

Principle operation of GPS with a GPS reference station Detailed DGPS method of operation

Detailed DGPS method of operation

Determining the correction values

Figure 38: Determining the correction values Relaying the correction values

Figure 39: Relaying the correction values 7.2.1.3 Correcting measured pseudo-range

Figure 40: Correcting measured pseudo-range Correcting measured pseudo-range DGPS based on carrier phase measurement

(Figure)

BLOCK DIAGRAM:

L.C.D

GPS MODEM

MAX 232

Micro controller unit

MAX 232

RF TRANSMITER

RF RECEIVER

Schematic:

COMPUTER SYSTEM

A Microcontroller is a single-chip microcomputer that contains all the components such as the CPU, RAM, some form of ROM, I/O ports, and timers. Unlike a generalpurpose computer, which also includes all of these components, a microcontroller is designed for a very specific task -- to control a particular system. Microcontrollers are sometimes called embedded microcontrollers, which just means that they are part of an embedded system. A microprocessor is a general-purpose digital computer with central processing unit (CPU), which contains arithmetic and logic unit (ALU), a program counter (PC), a stack pointer (SP), some working registers, a clock timing circuit, and interrupts circuits. The main disadvantage of microprocessor is that it has no on-chip memory. So we are going for micro controller since it has on-board programmable ROM and I/O that can be programmed for various control functions AT89S52 MICROCONTROLLER The microcontroller development effort resulted in the 8051 architecture, which was first introduced in 1980 and has gone on to be arguably the most popular micro controller architecture available. The 8051 is a very complete micro controller with a large amount of built in control store (ROM & EPROM) and RAM, enhanced I/O ports, and the ability to access external memory. The maximum clock frequency with an 8051 micro controller can execute instructions is 20MHZ. Microcontroller is a true computer on chip. The design incorporates all of the features found in a microprocessor: CPU, ALU, PC, SP and registers. It also has

the other features needed to, make complete computer: ROM, RAM, parallel I/O, serial I/O, counters and a clock circuit. The 89C51/89C52/89C54/89C58 contains a non-volatile FLASH program memory that is parallel programmable. For devices that are serial programmable (In-System Programmable (ISP) and In-Application Programmable (IAP) with a boot loader)All three families are Single-Chip 8-bit Microcontrollers manufactured in advanced CMOS process and are Derivatives of the 80C51 microcontroller family. All the devices have the same instruction set as the 80C51. 2.3 FEATURES • 8K Bytes of In-System Reprogrammable Flash Memory • Endurance: 1,000 Write/Erase Cycles • Fully Static Operation: 0 Hz to 33 MHz • Three-level Program Memory Lock • 256 x 8-bit Internal RAM • 32 Programmable I/O Lines • Three 16-bit Timer/Counters • Eight Interrupt Sources • Programmable Serial Channel • Low-power Idle and Power-down Modes 2.4 DESCRIPTION: The AT89s52 is a low power, high performance CMOS 8-bit micro computer with 8K bytes of flash programmable and erasable read only memory(PEROM).The device is manufactured using Atmel’s high density nonvolatile memory technology and is compatible with the industry standard 80c51 and 80C52 instruction set and pin out. The on-chip flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with flash on a monolithic chip, the Atmel AT89s52 Is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The main advantages of 89s52 over 8051 are

 Software Compatibility  Program Compatibility  Rewritability

The 89s52 microcontroller has an excellent software compatability, i.e. the software used can be applicable to any other microcontroller. The program written on this microcontroller can be carried to any base. Program compatibility is the major advantage in 89s52. The program can be used in any other advanced microcontroler.

The program can be reloaded and

changed for nearly 1000 times. 2.4.1 89s52 PROCESSOR ARCHITECTURE:

The AT89s52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full-duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89s52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt

system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next hardware reset. 2.4.3 PIN DESCRIPTION: VCC Supply voltage. GND Ground. Port 0 Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs. Port 0 can also be configured to be the multiplexed lower order address/data bus during accesses to external program and data memory. In this mode, P0 has internalpullups.Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pullups are required during program verification. Port 1 Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2

GPS receivers require different signals in order to function (Figure42). These variables are broadcast after position and time have been successfully calculated and determined. To ensure that the different types of appliances are portable thereareeitherinternationalstandards for data exchange (NMEAandRTCM), or the Manufacturer provides defined (proprietary) formats and protocols.

Block diagram of a GPS receiver with interfaces Data interfaces The NMEA-0183 data interface In order to relaycomputedGPSvariablessuchasposition, velocity, courseetc.toaperipheral(e.g. computer, screen, transceiver),GPSmoduleshaveaserialinterface(TTLorRS -232level).The mos t importantelements of receiverinformationarebroadcastviathisinterfaceinaspecialdataformat. ThisformatisstandardisedbythenationalMarineElectronicsAssociation (NMEA)toensurethatdataexchangetakesplacewithoutanyproblems.Nowadays,dataisrela yedaccordingtotheNMEA0183specification.NMEAhasspecifieddatasetsforvariousapplications e.g. GNSS(Global Navigation Satellite System),GPS, Loran,Omega, Transit andalso forvariousmanufacturers.ThefollowingsevendatasetsarewidelyusedwithGPSmodulestor elayGPSinformation[xv]:

1. GGA(GPSFixData,fixeddatafortheGlobalPositioningSystem) 2. GLL(GeographicPosition–Latitude/Longitude) 3. GSA(GNSSDOPandActiveSatellites,degradation of accuracy and thenumberof active satellites intheGlobalSatelliteNavigationSystem) 4.GSV(GNSSSatellitesinView,satellitesinviewintheGlobalSatelliteNavigationSystem) 5. RMC(RecommendedMinimumSpecificGNSSData) 6.VTG(CourseoverGroundandGroundSpeed,horizontalcourseandhorizontalvelocity) 7. ZDA(Time&Date) Structure of the NMEA protocol InthecaseofNMEA,therateatwhichdataistransmittedis4800Baudusingprintable8bitASCII characters. Transmissionbeginswithastartbit(logicalzero),followedbyeightdatabitsandastopbit(logic alone)added attheend.Noparitybitsareused.

NMEA format (TTL and RS-232 level) ThedifferentlevelsmustbetakenintoconsiderationdependingonwhethertheGPSreceiverus edhasaTTLor RS-232interface(Figure)

•InthecaseofaTTLlevelinterface,alogicalzerocorrespondstoapprox.0Vandalogicalonerou ghlyto theoperatingvoltageofthesystem(+3.3V..+5V) •InthecaseofanRS232interfacealogicalzerocorrespondstoapositivevoltage(+3V_._+15V) anda logicaloneanegativevoltage(-3V...–15V). If a GPS module with a TTL level interface is connected to an appliancewith an RS-232 interface,a level conversionmustbeeffected_ AfewGPSmodulesallowthebaudratetobeincreased(upto38400bitsper_second). EachGPSdatasetisformedinthesamewayandhasthefollowingstructure: $GPDTS,Inf1,Inf2,Inf3,Inf4,Inf5,Inf6,Infn*CS ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable8

Table 8: Description of the individual NMEA DATA SET blocks The maximum number ofcharacters_used_must_not_exceed_79._For_the_purposes_of_determining_this_num ber,_the_ Start sign $and endsigns are notcounted. Thefollowing NMEA Protocol was recorded using a GPS receiver(Table9):

Recording of an NMEA protocol GGA data set The GGAdataset(GPSFixData)containsinformationontime,longitudeandlatitude,thequalityof thesystem, Thenumberofsatellitesusedandtheheight. AnexampleofaGGAdataset: $GPGGA, 130305.0,4717.115,N,00833.912,E,1,08,0.94,00499,M,047,M,,*58 ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable10

Description of the individual GGA data set blocks GLL data set TheGLLdataset (geographic position–latitude/longitude) containsinformationonlatitudeandlongitude,time And health. ExampleofaGLLdataset: $GPGLL,4717.115,N,00833.912,E,130305.0,A*32 ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable

Description of the individual GGL data set blocks GSA data set TheGSAdataset (GNSSDOPandActiveSatellites)containsinformationonthemeasuringmode(2Dor3D),the number of satellites used to determine the position and theaccuracy ofthemeasurements (DOP:Dilution of Precision). AnexampleofaGSAdataset: $GPGSA,A,3,13,20,11,29,01,25,07,04,,,,1.63,0.94,1.33*04 ThefunctionoftheindividualcharacterorsetsofcharactersisdecribedinTable

Description of the individual GSA data set blocks GSV data set The GSV data set (GNSS Satellites in View) contains information on the number of satellites in view, there Identification, theirelevationandazimuth,andthesignal-tonoiseratio. AnexampleofaGSVdataset:_ $GPGSV,2,2,8,01,52,187,43,25,25,074,39,07,37,286,40,04,09,306,33*44 ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable13.

Description of the individual GSV data set blocks RMC data set TheRMCdata set (RecommendedMinimumSpecificGNSS) contains informationontime, latitude, longitude And height, systemstatus, speed, courseanddate.ThisdatasetisrelayedbyallGPSreceivers. AnexampleofanRMCdataset:_ $GPRMC,130304.0,A,4717.115,N,00833.912,E,000.04,205.5,200601,01.3,W*7C

ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable

Description of the individual RMC data set blocks VTG data set TheVGTdataset(CourseoverGroundandGroundSpeed)containsinformationoncourseands peed. AnexampleofaVTGdataset: $GPVTG,014.2,T,015.4,M,000.03,N,000.05,K*4F ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable

Description of the individual VTG data set blocks ZDA data set The ZDA dataset(timeanddate)contains informationonUTCtime,the dateandlocaltime. AnexampleofaZDAdataset: $GPZDA,130305.2,20,06,2001,,*57 ThefunctionoftheindividualcharactersorcharactersetsisexplainedinTable

Description of the individual ZDA data set blocks Calculating the checksum The checksumisdeterminedbyanexclusiveoroperationinvolvingall8databits (excludingstartandstopbits) Fromalltransmittedcharacters, including separators. The exclusiveor operation commences afterthe startofthe dataset($sign)andendsbeforethechecksumseparator(asterisk:*). The8-bit result is divided into 2 sets of 4 bits (nibbles) and each nibble is converted into the appropriate Hexadecimal value(0...9,A...F).ThechecksumconsistsofthetwohexadecimalvaluesconvertedintoASCII characters. Theprincipleofchecksumcalculationcanbeexplainedwiththehelpofabriefexample: ThefollowingNMEAdatasethasbeenreceivedandthechecksum(CS)mustbeverifiedforitsc orrectness. $GPRTE,1,1,c,0*07 (07 is_the_checksum) Procedure: 1. Onlythecharactersbetween$and*areincludedintheanalysis:GPRTE,1,1,c,0

2.These13ASCIIcharactersareconvertedinto8bitvalues(seeTable) 3.Eachindividualbitofthe13ASCIIcharactersislinkedtoanexclusiveoroperation(N.B.Ifthenumberofonesisuneven,theexclusive-orvalueisone) 4. Theresultisdividedintotwonibbles 5. Thehexadecimalvalueofeachnibbleisdetermined 6.BothhexadecimalcharactersaretransmittedasASCIIcharacterstoformthechecksum

Determining the checksum in the case of NMEA data sets Hardware interfaces Antenna GPS modulescan either be operated with a passive or active antenna. Active antenna, i.e. with abuiltinpreamplifier(LNA:LowNoiseAmplifier)arepoweredfromtheGPSmodule,thecurr

entbeingprovidedbytheHFsignaline.Formobilenavigationalpurposescombinedantennae( e.g.GSM/FMandGPS)aresupplied.GPS antennaereceiverighthandedcircularpolarisedwaves. Twotypesofantennaareobtainableonthemarket,PatchantennaeandHelixantennae.Patchant ennaeareflat,generallyhaveaceramicandmetallisedbodyandaremountedonametalbaseplat e.Inordertoensurea sufficiently high degree of selectivity, the base to Patch surface ratiohas tobeadjusted. Patchantennae are oftencastinahousing(Figure),[xxii]). Helixantennaearecylindricalinshape(Figure47,[xxiii])andhaveahighergainthanthePatcha ntennae.

Open and cast Patch antennae

Basic structural shape of a Helix antennae powerSupply

GPSmodulesmustbepoweredfromanexternalvoltagesourceof3.3Vto6Volts.Ineachcase,th epowerdraw isverydifferent. Time pulse: 1PPS and time systems MostGPS modules generate a timepulse every second, referred to as 1 PPs (1 pulse per second), which is synchronisedtoUTC.ThissignalusuallyhasaTTLlevel(Figure).

1PPS signal Thetimepulsecanbeusedtosynchronisecommunicationnetworks(PrecisionTiming). As time can play a fundamental part whenGPS is used to determine a position, a distinction is drawn here betweenfiveimportantGPStimesystems: Atomic time (TAI) The International AtomicTime Scale (Temps Atomique International) was introduced in order to provide a universal 'absolute' time scale that would meet various practical demands andat the sametimealso be of significanceforGPSpositioning.Since1967,thesecondhasbeendefinedbyanatomicconstan tinphysics,the non-radioactive element Cesium 133Cs being selected as a reference. The resonant frequency between the

Selected energy states of this atom has been determined at 9 192 631 770 Hz. Time defined in this way is Therefore part of the SIsystem(System International).Thestartofatomictimetookplaceon01.01.1958at 00.00hours. 8.3.3.2 Universal time co-ordinate (UTC) UTC (Universal Time Coordinated)was introduced, in order to have a practical time scale that was oriented towardsuniversalatomictimeand,atthesametime,adjustedtouniversalcoordinatedtime.Itisdistinguished from TAIin theway the seconds are counted, i.e.UTC = TAl - n,where n= complete seconds that can be alteredon1stJanuaryor1stJuneofanygivenyear(leapseconds). 8.3.3.3 GPS time GeneralGPSsystemtimeisspecifiedbyaweeknumberandthenumberofsecondswithinthatw eek.Thestart datewasSunday,6thJanuary1980at0.00hours(UTC).EachGPSweekstart in the night from Saturday to Sunday, thecontinuoustimescalebeingsetbythemainclockattheMasterControlStation. ThetimedifferencethatarisesbetweenGPSandUTCtimeisconstantlybeingcalculatedandap pendedtothenavigationmessage. 8.3.3.4 Satellite time Because of constant, irregular frequency errors in the atomic clocks on board the GPS satellites, individual SatellitetimeisatvariancewithGPSsystemtime. Thesatelliteclocksaremonitoredbythecontrolstationand Any apparent time difference relayed to Earth. Any time differences must be taken into account when Conducting localGPSmeasurements 8.3.3.5 Local time

Local time is the time referred to within a certain area. The relationship between local time and UTCtime is Determined bythetimezoneandregulationsgoverningthechangeoverfrom_normal_timetosummertime Example of a timeframe(Table20)on21stJune2001(Zurich)

. Table 20: Time systems The interrelationship of time systems (valid for 2001): TAI-UTC=+32sec GPS-UTC=+13sec TAI–GPS=+19sec 8.3.4 Converting the TTL level to RS-232 8.3.4.1 Basics of serial communication ThepurposeoftheRS-232interfaceismainly • to link computers to each other(mostly bi-directional) • Tocontrolserialprinters • ToconnectPCstoexternalequipment, suchasGSMmodems,GPSreceivers,etc. Theserialports inPCsaredesigned forasynchronoustransfer. Personsengagedintransmittingandreceiving

Operationsmustadheretoacompatibletransferprotocol, i.e.anagreementonhowdataistobetransferred. Bothpartnersmustworkwiththesameinterfaceconfiguration, andthiswillaffecttherateoftransferme asured Inbaud.Thebaudrateisthenumberofbitspersecondtobetransferred.Typicalbaudratesare110 , 150,300, 600,1200,2400,4800,9600,19200and38400baud,i.e.bitspersecond.Theseparametersarela iddownin the transfer protocol. In addition, both sides on what checks should be must reach agreement Implementedregardingthereadytotransmitandreceivestatus. During transmission, 7 to 8 data bits arecondensedinto a data word in order to relay the ASCII codes. The lengthofadatawordislaiddowninthetransferprotocol. The beginning of data word is identified by a startbit,and at theend of everyword1 or 2 stopbitsareAppended. Acheckcanbecarriedoutusingaparitybit.Inthecaseofevenparity, theparitybitisselectedinsuchawayThatthetotalnumberoftransferreddataword»1bits«iseve n(inthecaseofunevenparitythereisanunevennumber).Checkingparityisimportant,becausei nterferenceinthelinkcancausetransmissionerrors.Even if onebitofadatawordisaltered,theerrorcanbeidentifiedusingtheparitybit. 8.3.4.2 Determining the level and its logical allocation DataistransmittedininvertedlogicontheTxDandRxDlines.TstandsfortransmitterandRforre ceiver. Inaccordancewithstandards,thelevelsare: • Logical0=positivevoltage, transmitmode:+5..+15V,receivemode:+3..+15V • Logical1=negativevoltage, transmit_mode:-5..-15V,receivemode-3..-15V The difference between the minimum permissiblevoltageduring transmission_ andreceptionmeans that line Interference doesnot affect the function of the interface, provided thenoiseamplitudeis_below2V.

ConvertingtheTTLleveloftheinterfacecontroller (UART,universal asynchronousreceiver/transmitter)totherequiredRS232levelandviceversaiscarriedoutbyalevelconverter(e.g.MAX3221andmanymorebeside s). Thefollowingfigure (Figure) illustrates the difference betweenTTL and RS232levels.Levelinversion can clearly be seen.

Difference between TTL and RS-232 levels Converting the TTL level to RS-232 Many GPS receivers and GPS modulesonlymakeserialNMEAand proprietarydataavailable using TTL levels (approx.0Vorapprox.Vcc=+3.3Vor+5V).It is not always possible toevaluate this data directly through a PC,as a PCinputrequiresRS232levelvalues. Asacircuitsneededtocarryoutthenecessaryleveladjustment,theindustryhasdeveloped integrated circuits Specifically designed todeal with conversion between the two level ranges, to undertake signal inversion ,and to accommodate the necessary_equipment to generate negative supply voltage(by_meansof built-incharge pumps)._ A complete bidirectional levelconverter that usesa"MaximMAX3221"[xxiv] is illustrated on the followingCircuit

diagram(Figure_50).Thecircuithasanoperationalvoltageof3V...5V_and_is_protectedagai nstvoltage peaks(ESD)of±15kV.ThefunctionoftheC1..C4capacitorsistoincreaseorinvertthevoltage.

Block diagram pin assignment of the MAX32121 level converter Thefollowing test circuit(Figure) clearly illustrates the way in which the modules function.In the case of thisconfiguration,aTTLsignal(0V...3.3V)isappliedtolineTIN.Theinversionandvoltageincr easeto±5VcanbeseenonlinesTOUTandRINoftheRS232output.

Functional test on the MAX3221 level converter Basics of GPS handheld receivers AGPSreceivercanbedividedintothefollowingmainstages(Figure52).

Simplified block diagram of a GPS receiver

• Antenna: The antenna receives extremelyweak satellitesignals on afrequency of 1572.42MHz. Signal outputisaround–163dBW.Some(passive)antennaehavea3dBgain. • LNA 1:Thislownoiseamplifier(LNA)amplifiesthesignalbyapprox.15...20dB. GPS_Basics u-bloxag_ GPS-X-02007 • HF filter: TheGPSsignalbandwithisapprox2MHZ.TheHFfilterreducestheaffectsofsignalinterferenc e. TheHFstageandsignalprocessoractuallyrepresentthespecialcircuitsinaGPSreceiverandar eadjustedtoeachother. • HF stage: The amplified GPSsignalismixedwiththefrequencyofthelocaloscillator.ThefilteredIFsignalis maintaine data constant level in respect fits amplitude anddigitalisedviaAmplitude GainControl(AGC) • IF filter: The intermediate frequency is filtered out using bandwidthof2MHz.Theimage frequencies arising at the mixing stage are reduced to a permissible level. • Signal processor: Up to16different satellite signals can be correlated and decoded at the same time CorrelationtakesplacebyconstantcomparisonwiththeC/Acode.TheHFstageandsignalproc essorare simultaneously switched to synchronies with the signal. The signal processor has its own time base (Real Time Clock, RTC). All the data ascertained is broadcast (particularlysignaltransit time to the relevant Satellites determined bythecorrelator),and this is referredtoassourcedata.ThesignalprocessorcanbeOffsetbythecontrollerviathecontrollinet ofunctioninvariousoperatingmodes. • Controller: Usingthesourcedata, thecontrollercalculatesposition, time, speed and course etc.It controls The signal processor and relays the calculated values to the

display. Important information (such asEphemeris, the most recent position etc.)Are decoded and saved in RAM. The program and the calculation Algorithms are saved in ROM. • Keyboard: Usingthekeyboard, theusercanselect, whichcoordinatesystemhewishestouseandwhich Parameters (e.g.numberofvisible satellites) should be displayed. Display: Thepositioncalculated (longitude,latitude and height)mustbemadeavailabletotheuser.This can either be displayed using a 7-segment displayer shown on screen usingaprojectemap.Thepositionsdeterminedcanbesaved,wholeroutesbeingrecorded._ • Current supply: The powersupplydeliversthenecessary operational voltage to all levels of electronic component. GPSBasics_u-bloxag GPS-X-02007 Page73 GPS receivermodules Basic design of a GPS module GPS moduleshavetoevaluateweakantennasignalsfromatleastfoursatellites, in order to determine a correct three dimensional position. Atimesignalisalsooftenemittedinadditiontolongitude, latitudeandheight. Thistime signal is synchronized with UTC (UniversalTimeCoordinated). Fromthepositiondeterminedandtheexacttime, additionalphysicalvariables, suchasspeedandaccelerationcanalsobecalculated. TheGPSmoduleissuesinformationontheconstellation,satellitehealth,andthenumberof visible satellitesetc.

Figure 53: Typical block diagram of a GPS module The signal ls received(1575.42MHz)are pre-amplified and transformed to a lower r intermediate frequency. Thereferenceoscillatorprovidesthenecessarycarrierwaveforfrequencyconversion, alongwiththenecessaryclockFrequency for the processor and correlator.The analogueintermediatefrequency_is converted into adigitalSignalbymeansofa2-bitADC. SignaltransittimefromthesatellitestotheGPSreceiverisascertainedbycorrelatingPRNpulse sequences. TheSatellitePRNsequencemustbeusedtodeterminethistime, otherwisethereisnocorrelationmaximum. DataisrecoveredbymixingitwiththecorrectPRNsequence. Atthesametime, theusefulsignalisamplifiedabovetheinterferencelevel [xxv]. Upto16satellitesignalsareprocessedsimultaneously.Thecontrolandgenerationof PRNsequencesandtherecoveryofdataiscarriedoutbyasignalprocessor.Calculatingandsavi ngtheposition,

includingthevariablesderivedfromthis,iscarriedoutbyaprocessorwithamemoryfacility.

WHAT IS RADIO FREQUENCY? Radio Frequency (RF) does not refer just to radio broadcasting but rather encompasses all of the electromagnetic spectrum. RF energy is classified according to frequency. The range of frequencies is called the Radio Spectrum. While there is no precise beginning or end to frequencies making up the RF spectrum, Figure 1 shows the generally accepted ranges and class designations. Transmitter and receiver be within sighting distance of each other

Carrier Wave How do we send information in a radio signal? Carrier wave ● An RF signal – usually a sinusoid – that carries information ● Carrier is usually a much higher frequency than the information itself! ● Ex: 2.4 GHz 802.11b networks carry a lot less than 2.4 GBit/sec of data.... ● Rather, carry up to 11 MBit/sec of information ● Why use a carrier?? ● Easier to generate a sinusoid signal, and it will travel further. Carrier wave frequency ● The frequency of a radio transmission is the center frequency of the carrier ● Actual frequency of the carrier changes over time, e.g., with FM transmission

Radio Frequency (RF) refers specifically to the electromagnetic field, or radio wave, that is generated when an alternating current is input to an antenna. This field can be used for wireless broadcasting and communications over a significant portion of the electromagnetic radiation spectrum -- from about 9 kilohertz (kHz) to thousands of gigahertz (GHz) -- referred to as the RF spectrum. As the frequency is increased beyond the RF spectrum, electromagnetic energy takes the form of infrared, visible light, ultraviolet,

x

rays

and

gamma

rays.

Many types of wireless devices make use of RF fields: radio, television, cordless phones, cell phones, satellite comm systems, and many measuring and instrumentation systems used in manufacturing. Some wireless devices, such as remote control boxes and

cordless

mice,

operate

at

infrared

or

visible

light

frequencies.

The RF spectrum is divided into several ranges, or bands. Each of these bands, other than the lowest frequency segment, represents an increase of frequency corresponding to an order of magnitude (power of ten). FCC rules, combined with the continuing evolution of digital technology, sparked the development of spread spectrum data communication radios. These radios offer significant performance and operation benefits

to

end-users.

The conventional radio signal which these devices use is referred to as narrow-band, which means that it contains all of its power in a very narrow portion of the radio frequency bandwidth. Due to the relatively small portion of the radio band that an individual radio transmission occupies, the FCC has traditionally favored these conventional radios. However, as a result of the very narrow frequency, these radios are often prone to interference (a single interfering signal at or near their frequency can easily

render

the

radio

inoperable).

Spread spectrum is a technique that takes a narrow band signal and spreads it over a broader portion of the radio frequency band, offering the operational advantage of being resistant it interference. Spread spectrum radios are inherently more noiseimmune than conventional radios. Thus they will operate with higher efficiency than conventional

technology.

In performing spread spectrum, the transmitter takes the input data and spreads it in a

predefined method. Each receiver must understand this predefined method and despread the signal before the data can be interpreted. There are two basic methods to performing the spreading: frequency hopping (FHSS) and direct sequence (DSSS). FHSS spreads its signals by "hopping" the narrow band signal as a function of time. DSSS its signal by expanding the signal over a broad portion of the radio band. The FCC allows the use of spread spectrum technology in three radio bands, 902-928 MHz, 2400-2483.5 MHz and 5752.5-5850 MHz for transmission under 1 Watt of power. This power limit prevents interference within the band over long distances. Spread spectrum requires no FCC site license; the FCC grants a one-time license on the radio product. After that license is granted, the product can be sold anywhere in the U.S HOW IS THE RF HARNESSED? In order for a signal to be transmitted wireless, it is necessary for the signal to be conveyed into free space then recovered and restored to its original form. Two devices are used to accomplish this task: the transmitter and the receiver.

Radio Frequency bands are allocated for various purposes by the International Telecommunication Union Radio communication sector (ITU-R), an agency Within the United Nations (UN). The Federal Communications Commission (FCC) is a member of the ITU-R along with other similar agencies representing their respective government. Their goal is to manage the finite resources of the RF spectrum and satellite orbital positions. In doing so they have allocated sub bands of the RF spectrum for use in Satellite communications. For the purpose of this document we will only focus on two of these sub bands: “C” and “Ku”.They are the most commonly used in commercial satellite communications. C-BAND The frequency range allocated for C-band is 3.7GHz – 6.425GHz. It is further divided into separate halves, one for ground-to-space links (Uplink) and one for space-toground links (downlink) as shown: C-band Uplink Frequencies: 5.925GHz – 6.425GHz C-Band Downlink Frequencies: 3.7GHz – 4.2GHz KU-BAND The frequency range allocated for Ku-band is 11.7GHz – 14.5GHz. Ku-band, like Cband, is further divided into separate halves, one for ground-to-space links (Uplink) and one for space-to-ground links (downlink) as shown: Ku-Band Uplink Frequencies: 14GHz – 14.5GHz

Ku-Band Downlink Frequencies: 11.7GHz – 12.2GHz Although the international satellite communication frequency bands are similar to the U.S. frequency bands, there are some variances; specifically the use of extended C and extended Ku bands that are in use by satellites as well as others. POLARIZATION Polarization is another property of electromagnetic waves. It can be manipulated into two types of polarization: Linear (Vertical and Horizontal) and Circular (Right-Hand and Left-Hand) polarizations. Linear polarization is commonly used on satellites. Figure 3 shows the orientation that the electric field of an electromagnetic wave would take depending on the capabilities and orientation of an antenna

Polarization The most important application of polarization is in frequency reuse. This is Where two electromagnetic waves, one traveling on the vertical plane and the other in the horizontal plane, are using the same frequency without impacting one another. This gives the ability to essentially double the amount of frequencies available for use.

The Transmitter The function of a transmitter is to take an analog or digital signal and, through an antenna, deliver it into free space. A simple transmitter is illustrated below.

You will notice the transmitter has three primary components: a frequency source (the oscillator), a gain stage (the amplifier) and a free space coupler (the antenna). The oscillator generates the frequency at which the transmitter will operate. This frequency is called the Fundamental. In order for the fundamental frequency to be transmitted effectively through the resistance of free space, it is necessary for the signal to be amplified. This is the purpose of the gain stage. Once the oscillator’s frequency has been amplified, it must transition from being a frequency contained within conductors (called transmission lines) into free space. This is the function of the antenna. The transmitting antenna allows the RF energy to be efficiently radiated from the output stage into free space. It is, in essence, a bridge between a guided wave and free space. WHAT IS MODULATION? Now that you have a basic understanding of how a signal finds itself delivered into free space, you may be wondering how any useful information could be represented by that signal. The answer is Modulation. Modulation is the process whereby a carrier medium is impressed with content. The frequency to be controlled is called the Carrier. A carrier is like a moving truck. Just as you might place the contents of your house on the truck, so the information you wish to transmit is loaded onto a carrier. That signal, which has been impressed onto the carrier for “transportation”, is called the Program or Control

Signal. In the case of digital data transmission, a carrier frequency is modulated with a control signal consisting of binary data.

The Receiver: The purpose of a receiver is to receive the modulated carrier, remove it, and recover the Original program signal. This process is called Demodulation. Figure 4 illustrates a single-conversion superhet AM receiver. While receiver topologies vary widely all involve several stages to affect the reception and recovery process. First, the receiving antenna Intercepts the electromagnetic waves radiated from the transmitting antenna. When these waves impinge upon the receiving antenna, they induce a small voltage in it. This voltage causes a weak current to flow, which contains the same frequency as the original current in the transmitting antenna. That current is amplified to a more useable level and then fed into a device called a mixer. The mixer takes this incoming signal and combines it with anon-board frequency source called a local oscillator. This converts the signal to a new lower frequency called the Intermediate Frequency or IF for short. The detector then strips out the IF frequency and leaves present only the original information.

By now you should have a basic, but clear, understanding of how information signals are transmitted and received. With that as a foundation, you are now ready to consider the steps involved in putting RF to work for you. CHOOSE A FREQUENCY OF OPERATION To go somewhere you choose a road on which to travel. So, too, must you select a frequency on which your information signal will travel. This is a difficult task as there are many diverse issues involved. Here are a number of the most critical to consider. Propagation Characteristics The transfer of energy through space is called Propagation. In general, radio wave propagation is divided into three broad categories: (1) Ground Wave propagation, where the signal travels through or along the earth’s surface; (2) Line-of-Sight, where the wave travels almost like a beam of light in a straight line and thus requires that the transmitter and receiver be within sighting distance of each other;

(3) Sky Wave propagation, where the signal travels primarily through the air via reflections from the ionosphere. It is important to consider the physical environment In which the device will operate in order to determine if the frequency you have chosen Possesses useable propagation characteristics. For example, transmission through walls would be highly attenuated and poorly served by frequencies in the microwave region, while effective transmission through water might require selection of a frequency in the VLF range.

Propagation Basics The propagation of radio waves in 802.11 applications is characterized by several factors: Signal power is diminished by geometric spreading of the wavefront,commonly known as free space loss

Signal power is attenuated as the wave passes through solid objects such as trees, walls, window and the floors of buildings The signal is scattered and can interfere with itself if there are objects in the beam of the transmit antenna even if these objects are not on the direct path between the transmitter and the receiver Free space loss. Geometric spreading happens because the wavefront radiated signal energy expands like a big column as a function of the distance from the transmitter. When the distance from the transmitter is measured in units of the signal wavelength (λ), the free space loss (Lfsl) in signal power at a distance (r) from the transmitter is: Lfsl = r2 (4π)2/λ2 Eq 1 Using decibels to express the loss and using 2.45GHz as the signal frequency for 802.11b/g APs, the equation can be simplified to: Lfsl = 40 + 20*log (r) Eq 2 Where Lfsl is expressed in dB and r is expressed in meters. Attenuation. When the RF signal passes though solid objects, some of the signal power is absorbed. The most convenient way to express this is by adding an “allowed loss” to the Free Space loss. Attenuation can vary greatly depending upon the structure of the object the signal is passing through. Metal in the barrier greatly increases the attenuation. Thickness also increases the loss. General rules of thumb on attenuation are: Trees account for 10 to 20 dB of loss per tree in the direct path. Loss depends upon the size and type of tree. Large trees with dense foliage create greater loss. Walls account for 10 to 15 dB depending upon the construction. Interior walls are on the low end and exterior walls, especially those with stucco, create more loss. Floors of buildings account for 12 to 27 dB of loss. Floors with concrete and steel are at the high end and wood floors are at the low end. Mirrored walls have very high loss because the reflective coating is conductive. Scattering. RF signals can reflect off of many things and the direct signal combines with signals that have reflected off of objects that are not in the direct path. This effect is usually described as multipath, fading, Rayleigh fading or signal dispersion.

When RF signals combine they can be distorted. The distortion degrades the ability of the receiver to recover the signal in a manner much like signal loss. While a great deal of research has gone into the characterization of signal scattering, a simple and common way of applying the effects of scattering is to change the exponent on the distance factor in Equation 1. When the Free Space Loss, Attenuation and Scattering are combined the loss is: L = rn (4π)2/λ2 + Lallowed Eq 3 Expressed in decibels: L (dB) = 40 + 10*n*log (r) + Lallowed Eq 4 One difficulty in using the exponent to model the effect of scattering is that the exponent tends to increase with range in an environment with a lot of scattering. Calculating a range can often require some iteration of the exponent to be used. Link Margin. In addition to environmental factors described above, the performance of any communication link depends on the quality of the equipment being used. Link margin is a way of quantifying equipment performance. An 802.11 communication link has an available link margin that is determined by four factors: Transmit power Transmit antenna gain Receive antenna gain Minimum received signal strength or level. The link margin is: Lmargin = TXpower + TXant gain + RXant gain – RSL Eq 5 The link factors are usually listed in the manufacture’s data sheets for the equipment being used. For instance, if Sputnik’s AP160 is used as an access point with an external 8.5 dBi antenna to communicate with a laptop computer having a D-Link DWLG650station card, the factors to be used are:  TX power = 13 dBm  TX antenna gain = 8.5 dBi  RX antenna gain = 0 dBi  Min RSL = -89 dBm

 Link margin = 110.5 dB Note that the Min RSL is dependent upon rate and the 1 Mbps rate is used for maximum range. TX power can also be rate dependent but manufacturers rarely indicate this. Maximum range. The maximum range is achieved when the signal loss expressed in Equation 4 is less than the link margin expressed in Equation 5. The system operator needs to know the equipment parameters and must estimate the allowed loss and the scattering exponent to complete the calculation. Example parameters are shown in Tables 1 and 2. Table 1. Application Dependent Environment Parameters

For example, suppose a service provider wanted to provide coverage in a public park to customers using laptop computers using Sputnik’s AP 160 access points equipped with external 8.5 dBi gain antennas. We would estimate the allowed loss to be 10 dB if the park had a modest number of trees mixed with open spaces and use a scattering exponent of 3. From equation 5, the maximum loss (Lmargin) is 110.5 dB. To get the maximum range we would solve Eq 4 for range: 110.5 = 40 + 10*3*log (rmax) + 10 –> rmax = 102 meters Using the same equation to calculate the range assuming free space loss (where the exponent = 2, and allowed loss = 0) provides a rather different answer: 110.5 = 40 + 10*2*log (rmax) + 0 –> rmax = 3,264 meters This example shows that environmental factors can play a significant role in diminishing the signal strength. However, since choosing the exponent and allowed loss is partly a guessing game, and partly a recursive exercise, it is common practice to take

a few real-world measurements of range in the area of the deployment, using the equipment to be deployed. Such measurements will improve the estimate of the exponent and allowed loss used to calculate the “coverage area” described in the next section. Dividing the total area by the coverage per node provides the estimated density and total number of wireless nodes that should be deployed. Coverage Area. In the example above, the AP160 has an antenna with a 70° beamwidth and can effectively operate with a laptop to a range of 102 meters. The coverage area is approximately a 70° sector of a circle with a radius of 102 meters so the coverage area is 3,186 sq meters or about 0.8 acres. If we were to repeat the same exercise for the AP160 with an 8 dBi gain omni-directional antenna, the range would be reduced to 98 meters. However, the coverage area increases to 15,174 sq meters or about 3.8 acres. While directional antennas can increase the range of a communication link, their impact on coverage area is less clear. The decision to use a directional antenna is often made based upon convenience; it might be simpler to install an access point on the edge of the area to be covered rather than in the center

Area geometry. The area geometry for the directional and omni-directional antennas

is shown below.

-

Required Bandwidth The amount of information that can be transferred depends on the carrier frequency and variable bandwidth. The carrier frequency must be many times the required bandwidth, thus, applications such as video and data links, which require wide bandwidths, utilize requencies well into the microwave range. In general, the bandwidth should be as narrow as possible to accommodate the required information content. This yields the best immunity to noise and allows the highest possible system sensitivity. Power Consumption In battery-powered applications, power consumption is generally a critical issue. Surprisingly, the relationship between frequency and power consumption is often overlooked. Since propagation efficiency is reduced as frequency climbs, higher frequencies require more power to achieve range. Potential Interference The final component of frequency selection is to understand what potential interference sources your device will be up against in the real world. Interference is the presence of unwanted noise or signals that increases the difficulty of reception. You may find that

many frequencies suited to your application have a high level of interference present because of their broad popularity. Interference can be divided into three primary categories: natural noise, man-made noise, and man-made signals. Natural noise originates in space and the earth's atmosphere. It tends to be greater at low frequencies. Man-made noise is caused by unintentional RF radiation from man-made devices, such as motors, switching power supplies and microwaves. Man-made signals are intentional RF emissions such as radio, television, cellular, etc. Immunity to noise depends on bandwidth and the frequency accuracy of the transmitter. The more accurate a signal’s frequency and the narrower a signal’s bandwidth, the narrower the receiver’s front-end filter can be. This increases the ratio between the signal and noise and greatly reduces

the potential for off-frequency interference. Figure 6 illustrates how a receiver with a narrow front end band pass opening (A) has a much better chance of receiving the incoming signal than receiver (B) with its wide front end band pass opening. DEVELOP RF REQUIREMENT SPECIFICATIONS This specification is simply a list of characteristics you feel are important. It will act as a roadmap during your consideration of the various RF solutions that are available. You will want to list particulars, such as preferred operational voltages, power consumption requirements, data rates, range requirements and frequency choices.

CHOOSE AN ANTENNA The antenna choice is critical in determining the overall performance and legality of a system. There are many issues related to understanding and selecting an antenna, which are covered in Linux application note #00500. It should be noted here, however, that as frequency increases antenna length is reduced. In some applications a large Antenna element is unsuitable for size or cosmetic reasons. This requires the designer to use a high operational frequency or create a unique antenna solution.

Working with the Garmin Interface Table of Contents •

Introduction

•

Hardware connection

•

NMEA mode

•

Garmin mode

•

DGPS mode

•

Text mode Introduction

All Garmin gps receivers support a computer interface. This can be used to backup the waypoints and routes on a computer and to provide real time display information on a computer screen. In addition Garmin supports differential gps input signals. The modes supported by Garmin receivers are given in the table below. All of the Interface Modes E-

E-

Y Y Y Y

map Y Y Y Y

trex Y Y Y N

Y

Y

Y

Y

Y Y

Y Y

Y Y

Y Y

Text Out

N

N

Y Y III+,

control . DGPS input only

Y

Y

1200 2400 4800 9600

RTCM/Text

N

N

Y

Y

.

Y

Y

N

N

.

Interface Mode

38/40/45XL 12/12XL/48 III/III+

None Garmin None/NMEA NMEA/NMEA

Y Y Y Y

Y Y Y Y

Garmin DGPS

Y

RTCM/NMEA RTCM/None

NMEA 0180, 0182, 0183 1.5

12Map III+, 12Map N

Notes . AKA GRMN/GRMN NMEA out 0183 2.0 NMEA in/out Has Garmin Interface

Be sure that you have selected the correct mode and baud rate for the program or unit you are trying to interface with. This is the main problem with interface failures. For all moving map programs you will likely need NMEA mode with the baud rate set to 4800. For programs that upload and download data you should probably be in Garmin mode with the baud rate set to 9600. Some digital cameras will need text mode with a baud rate of 9600. In all cases set the data width to 8, no parity, and 1 stop bit. Make sure the interface mode is selected in the program and the correct COM port is selected. Hardware Connection The hardware interface for Garmin units meets the NMEA requirements and is sufficient to drive 3 NMEA loads. It is also compatible with most computer serial ports using RS232 protocols. The interface speed can be adjusted as needed by the particular interface but it usually set automatically to the appropriate setting when the interface selection is made. There is only a data in and data out line with ground. There are are no handshake lines nor should you attempt to set up a software handshake using xon/xoff as the unit does not recognize this and may interfere with binary data uploads and downloads. In order to use the hardware interface you will need a cable. See the accessories chapter for the available cables. In some dedicated applications you may need to wire your own or perhaps you would just prefer to do that. The Garmin cable connector shown below will work for all of the handheld gps units except the etrex and emap.

Garmin gps receivers may be used to interface with other NMEA devices such as autopilots, fishfinders, or even another gps receivers. They can also listen to Differential Beacon Receivers that can send data using the RTCM SC-104 standard. Some of the latest computers no longer include a serial port but only a USB port. Garmin receivers are known to work with Serial to USB adapters and serial ports attached via the pcmcia (pc card) adapter. NMEA The National Marine Electronics Association has developed a specification that defines the interface between various marine electronic equipment. The standard permits marine electronics to send information to computers and to other marine equipment. GPS receiver communication is defined within this specification. Most computer programs that provide real time position information understand and expect data to be in NMEA format. This data includes the complete PVT (position, velocity, time) solution computed by the GPS receiver. The idea of NMEA is to send a line of data called a sentence that is totally self-contained and independent from other sentences. There are standard sentences for each device category and there is also the ability to define proprietary sentences for use by the individual company. All of the standard sentences have a two-letter prefix that defines the device that uses that sentence type. For gps receivers the prefix is GP. This is followed by a three-letter sequence that

defines the sentence contents. In addition NMEA permits hardware manufactures to define their own proprietary sentences for whatever purpose they see fit. All proprietary sentences begin with the letter P and are followed with a letter that identifies the manufacturer controlling that sentence. For Garmin this would be a G. Each sentence begins with a '$' and ends with a carriage return/line feed sequence. The data is contained within this single line with data items separated by a comma. The data itself is just ASCII text and may extend over multiple sentences in certain specialized instances but is normally fully contained in one variable length sentence. An example sentence might look like: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,*42 With an interpretation as follows: GGA - Global Positioning System Fix Data 123519

Fix taken at 12:35:19 UTC

4807.038,N Latitude 48 deg 07.038' N 01131.000,E Longitude 11 deg 31.000' E 1

Fix quality: 0 = invalid 1 = GPS fix 2 = DGPS fix

08

Number of satellites being tracked

0.9

Horizontal dilution of position

545.4,M

Altitude, Meters, above mean sea level

46.9,M

Height of geoid (mean sea level) above WGS84 ellipsoid

(empty field) time in seconds since last DGPS update (empty field) DGPS station ID number *42

the checksum data, always begins with *

Each Data type would have its own interpretation that is defined in the NMEA standard. This particular sentence provides essential fix data. Other sentences may repeat some of

the same information but will also supply new data. Whatever is reading the data can watch for the data sentence that it is interested in and simply ignore whatever sentences that is doesn't care about. In the NMEA standard there are no commands to indicate that the gps should do something different. Instead each receiver just sends all of the data and expects much of it to be ignored. On NMEA input the receiver stores information based on interpreting the sentence itself. While some Garmin receivers accept NMEA input this could only be used to update a waypoint or similar task and not to send a command to the unit. There is no way to indicate whether the sentence is being read correctly or to re-send some data you didn't get. Instead the receiving unit just checks the checksum and ignores the data if the checksum isn't correct figuring it will be sent again sometime later. No error can be generated to the remote system. The NMEA standard has been around for many years and has undergone several revisions. The protocol has changed and the number and types of sentences may be different depending on the revision. All Garmin receivers understand the latest standard, which is called: 0183 version 2.0. This standard dictates a transfer rate of 4800 baud. Some Garmin receivers also understand older standards. The oldest standard was 0180 followed by 0182, which transferred data at 1200 baud. Some Garmin receivers also understand an earlier version of 0183 called version 1.5. Some Garmin units can be set to 9600 for NMEA output but this is only recommended if you have determined that 4800 works ok and then you can try to set it faster. If you are interfacing a Garmin unit to another device, including a computer program, you need to insure that the receiving unit is given all of the sentences that it needs. If it needs a sentence that Garmin does not send then the interface to that unit is likely to fail. The sentences sent by Garmin receivers include: NMEA 2.0 •

GPBOD bearing, origin to destination - earlier G-12's do not transmit this

•

GPGGA fix data

•

GPGLL Lat/Lon data - earlier G-12's do not transmit this

•

GPGSA overall satellite reception data

•

GPGSV detailed satellite data

•

GPRMB minimum recommended data when following a route

•

GPRMC minimum recommended data

•

GPRTE route data

•

GPWPL waypoint data (this is bi-directional)

NMEA 1.5 - some units do not support version 1.5 •

GPBOD bearing origin to destination - earlier G-12's do not send this

•

GPBWC bearing to waypoint using great circle route.

•

GPGLL lat/lon - earlier G-12's do not send this

•

GPRMC minimum recommend data

•

GPRMB minimum recommended data when following a route

•

GPVTG vector track and speed over ground

•

GPWPL waypoint data (only when active go to)

•

GPXTE cross track error

In addition Garmin receivers send the following Proprietary Sentences: •

PGRME (estimated error) - not sent if set to 0183 1.5

•

PGRMM (map datum)

•

PGRMZ (altitude)

•

PSLIB (beacon receiver control)

The new etrex summit sends a $HCHDG sentence for its compass output. This list is specific to the handheld units. Other Garmin units may send other sentences and some use proprietary sentences to send control commands to the units themselves. Note that Garmin converts lat/lon coordinates to the datum chosen by the user when sending this data. This is indicated in the proprietary sentence PGRMM. This can help programs that use maps with other datums but is not a NMEA standard. Be sure and set your datum to WGS84 when commuicating to other NMEA devices.

It is possible to just log view the information presented on the NMEA interface using a simple terminal program. If the terminal program can log the session then you can build a history of the entire session into a file. More sophisticated logging programs can filter the messages to only certain sentences or only collect sentences at prescribed intervals. Some computer programs that provide real time display and logging actually save the log in an ASCII format that can be viewed with a text editor or used independently from the program that generated it. NMEA has its own version of essential gps pvt (position, velocity, time) data. It is called RMC, The Recommended Minimum, which might look like: $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*43 With an interpretation as follows: RMC

Recommended Minimum sentence C

123519

Fix taken at 12:35:19 UTC

A

Status A=active

4807.038,N Latitude 48 deg 07.038' N 01131.000,E Longitude 11 deg 31.000' E 022.4

Speed over the ground in knots

084.4

Track angle in degrees True

230394

Date - 23rd of March 1994

003.1,W

Magnetic Variation

*43

The checksum data always begins with *

NMEA input Many of the Garmin units also support an NMEA input mode. While not too many programs support this mode it does provide a standardized way to update or add waypoint and route data. Note that there is no handshaking or commands in NMEA mode so you just send the data in the correct sentence and the unit will accept the data

and add or overwrite the information in memory. If the waypoint name is the same you will overwrite existing data but no warning will be issued. The sentence construction is identical to what the unit downloads so you can, for example, capture a WPL sentence from one unit and then send that same sentence to another unit but be careful if the two units support waypoint names of different lengths since the receiving unit might truncate the name and overwrite a waypoint accidentally. If you create a sentence from scratch you should create a correct checksum. Be sure you know and have set you unit to the correct datum. A WPL sentence looks like: $GPWPL,4807.038,N,01131.000,E,WPTNME*31 With an interpretation of: WPL

Waypoint Location

4807.038,N Latitude 01131.000,E Longitude WPTNME *31

Waypoint Name

The checksum data, always begins with * Garmin mode

Garmin mode is a bi-directional binary proprietary interface protocol that is used by Garmin and many third party vendors do communicate directly with a Garmin receiver. All of the handheld units understand Garmin protocol but may not understand or respond to a specific command in that protocol. For example, if you were to try and store altitude information in a waypoint on a unit that cannot store altitude information then this command would fail. Garmin mode includes a set of published API (Application Programming Interface) specifications and other commands that are not published or made public in any fashion except as used by a Garmin product. There are other commands that are not even used by a Garmin product and are probably used by internal test groups and custom test equipment at the Garmin factory. It is beyond the scope of this manual to describe the detailed interface specification. A manual describing the published interface specifications is available for downloading at the

Garmin site. In addition some of the undocumented commands and features are available from web sources. Some of the things that you might be able to do using Garmin protocol include: 1. Getting the version number of the software. 2. Finding out the capabilities of the unit. 3. Uploading or downloading waypoint data. 4. Uploading or downloading Track data. 5. Uploading or downloading Route data. 6. Uploading or downloading Almanac data. 7. Downloading the current gps time. 8. Downloading the current gps position. 9. Uploading a new release of the firmware. 10. Uploading Downloading a screen snapshot. 11. Receive a complete PVT solution in real time. Older multiplexing units cannot do many of the items in the list. Specifically they cannot do item 2, or any item beyond 8 in the above list. The G-12 family cannot do items above 9 but this could change with new firmware releases. User data backup The most often used capabilities include the backup of critical user data such as waypoints and routes. To do this you would need to secure a Garmin capable program. These are available from Garmin or several third party sources. There are programs for pc's running dos, or windows, for macs, for Unix, and for palm pilots. Once you have the correct program you can place your unit in Garmin mode and set the baud rate to 9600. Generally all programs accept this baud rate but some may support other rates and even change the rate. Cable the unit to the computer and make sure the computer program is set to the correct serial port and the baud rate to 9600. The standard serial port settings are 8N1, 8 bit data, no parity, 1 stop bit. Do not use xon/xoff since this may interfere with proper transfer of binary data. If the program cannot access the unit

then check to ensure some other program is not using the port (the palm sync program is notorious for this) and that the port is configured correctly. This protocol is binary and requires handshaking so all three wires need to be hooked up correctly. Perhaps a null model adapter may be required to get the receive and transmit signals hooked up properly. You cannot modify individual waypoints or routes using this interface. Instead you load the full set of routes or the full set of waypoints. If you wish to revise certain data you should download the full set and the revise the data you wish on your computer, clear all the waypoint data, and then reload the full set back. Otherwise you may get unpredictable results on some units. Most units will simply overwrite waypoints with the same name but the emap will create a new waypoint if the location is different. This can make updating a waypoint a bit frustrating. Similarly you load the full tracklog. On units with multiple tracklogs you may find them all concatenated together on download. Some programs may be able to upload saved logs directly but some may not. On units that support the uploading of maps the rule is similar. You must assemble all of the maps you wish to upload and then send them all at once replacing the previous upload. Of course, the data in the computer program need not originate in your gps. It is quite possible, in some programs, to import external data to the program for later uploading or to edit the data files directly to provide this new information. It is also useful to modify and add comment data to waypoints using a computer keyboard instead of toggling it in with the unit keypad. Be aware that waypoints are always interpreted as using the WGS-84 datum for this interface. Unit to Unit transfer One interesting use for this protocol is to transfer information between units. To do this you need a Garmin to Garmin cable (available from Garmin and other sources) to hook the two units together. One of the units is placed in Host mode and the other unit sends commands to upload and download data. The commands are shown on your units menu. They may include:

1. RQST/SEND ALL USR 2. RQST/SEND CFG - configuration 3. RQST/SEND PRX - Proximity alarm data 4. RQST/SEND RTE - Routes 5. RQST/SEND TRK - Track Log 6. RQST/SEND WPT - Waypoints 7. RQST/SEND ALM - Almanac The emap and etrex do not support this mode. Other units may not work correctly in this mode or may not support some commands. For example a G-III does not have proximity alarms. The G-38 and the G-12 can talk to each other but the G-38 will not be able to support waypoint icons and you can easily overflow the track log on a 38 with the tracklog on a 12. It is also possible to use a computer as an intermediary for this transfer by moving the data from the unit to the computer and then uploading it to the target platform. Some Palm pilot programs even support the host mode so that they can serve as a temporary storage point for gps user data. Firmware Upgrade Garmin releases firmware upgrades for all of their twelve channel units to fix bugs and to add functionality. These upgrades are available from the Garmin web site and are free so long as you agree with the terms and conditions. They come with the appropriate program for pc platforms and are only supported by Garmin. There is no third party source and users on Macintosh units will have to find a friend to do the upgrade or use a pc emulator. Be careful that you only try and use the firmware for you specific unit, or you could break your unit completely and have to send it back to Garmin for repair. The older multiplex units cannot be upgraded in this fashion and if needed they must be returned to Garmin for any upgrades. Be sure and read the instructions that accompany the upgrade at the Garmin site. To ensure success make sure you download the upgrade using a binary mode. It comes as a zip file so if it unzips correctly you can be sure you downloaded it correctly. Make

sure you have a good connection to the gps. Try one of the Garmin interface programs to backup your data. Generally an upgrade does not lose user data but this is not always the case so it is a good idea to back it up. Leave the unit in Garmin mode for the upgrade. Your pc baud rate should be set to "maximum rate" possible so that the program can increase the baud rate to minimize the download time. Expect to lose any customization that you may have performed on your unit. Be sure you have fresh batteries in the unit. Writing the firmware into the prom can use significant battery power and if the batteries are weak you may not get a good load or you may start out with a seemingly good load that will fail later. Do not abort the process once it has begun. It can take several minutes to do the upgrade so be patient. If the upgrade fails, try it again. You must get an good upgrade before your unit will be operational again. If you lose power or connection during the upgrade you may have a unit without any code at all. If you were to attempt to power up the unit it will tell you the firmware is missing. Some have reported that this happened some time later. Weak batteries that were not able to burn the new code in the machine usually cause this. To recover perform these steps: 1. Connect your cable to the computer. 2. Get the computer ready to load the firmware but don't press ENTER. 3. Turn on the GPS and then press the ENTER key on your computer. 4. Watch - The program should begin to load the new firmware If you are unsuccessful then call Garmin and arrange to return your unit for them to upgrade. If you feel that the upgrade has a bug in it and the older release is better you can generally use an earlier upgrade to downgrade your unit. Garmin generally does not keep older versions available but they are often available on the net from other users. PVT data Some of the Garmin receivers support a PVT mode as part of the Garmin mode. If you are using a computer program that supports this then you can remain in Garmin mode even while running your real time mapping application. You set your unit to Garmin

mode and then select this solution from the menus in the application. Delorme mapping products support this mode. This is an advantage in that you don't need to switch modes and you can leave your interface at 9600 baud, which makes the real time response a bit faster. The update interval is 1 second and this mode does not require handshaking nor does it support retransmission of data. The following data is typically included as part of the pvt structure in the D800 message: •

Alt - Altitude above WGS-84 ellipsoid

•

Epe - total predicted error (2 sigma meters)

•

Eph - horizontal position error

•

Epv - vertical position error

•

Fix - type of position fix

•

Tow - time of week (seconds)

•

Posn - lat/lon (radians)

•

East - velocity east (meters/sec)

•

North - velocity north (meters/sec)

•

Up - velocity up (meters/sec)

•

Msl_height - height of WGS-84 ellipsoid above MSL (meters)

•

Leap seconds - difference between gps time and UTC (seconds)

•

Wn_days - week number days

Undocumented modes The Garmin Interface specification defines much of the exact interface requirements for Garmin mode. However, there are many things that are in the interface that are not described in this manual. Garmin has indicated that these are for test purposes and are not to be used by customers. They may also be changed from release to release and may only work with a particular test setup. However, many of these modes have been discovered and decoded by third party programmers. Such additional features such as screen captures fall into this category. One vendor has actually managed to get the pseudo range data out of the Garmin 12 family and provides a post processing

capability with these units by collecting data on a pc in real time for later processing thereby opening the possibility of using this unit for surveying applications. DGPS mode All Garmin receivers support DGPS. DGPS is a method of improving accuracy your receiver by adding a local reference station to augment the information available from the satellites. This station transmits correction data in real time that is received by a separate box, called a beacon receiver, to send correction information to the gps receiver. Most folks fabricate a custom cable to work with the beacon receiver. Here is a diagram for a fairly complicated version, but you may not need a setup that is this complicated depending on what else you may be doing.

For simple dgps connections you can just wire a beacon receiver output signal along with its ground to the data input terminals of the gps. If you need to be able to control the beacon receiver from the gps receiver then you will also need to send the output for the gps receiver to the beacon receiver. A standard computer interface cable can usually be used for this connection. If you also need to talk to a pc at the same time things start to get a little more complicated. To talk to a pc in NMEA mode you can simply send the output of the gps to both units. Wire the output signal to the input on the computer and the input on the beacon receiver. There is sufficient power in the signal from the Garmin to drive both units and even a third item. Note if the beacon receiver doesn't need to receive commands from the gps then there is no reason to send the signal both

places but the ground wire is still needed. Finally if the gps needs to talk to the pc in Garmin mode and also the beacon receiver you will need a switch to permit the beacon receiver to transmit difference signals or the pc to interact with the gps. You won't be able to do both at the same time. This should not present any real problems since the bidirectional Garmin mode is used to upload and download waypoint, route, and track data, which do not need the beacon receiver to be operational. *** More to be supplied Text Mode Text mode is a simple output mode that supplies velocity and position information in real-time. Currently certain digital cameras to include this data on the picture primarily use this. In the future many other uses will be found for this mode, which requires very little processing on the part of the device receiving the data. An example is shown below. @000607204655N6012249E01107556S015+00130E0021N0018U0000 @yymmddhhmmss Latitude Longitude error Altitude EWSpd NSSpd VSpd Each item is of fixed length making parsing by just counting the number of characters an easy task. It is grouped by use permitting a digital camera, for example, to just read the first 30 characters and report the time and position. Some of the data will require some programming to make meaningful for most users; such has the speed, which is devided into the X, Y, and Z components. This is the only format that provides vertical speed, which should be a great boon for balloonists. A more formal description of the fields is: FIELD DESCRIPTION: Sentence start

WIDTH: 1

NOTES: Always '@'

T I M E

Year Month Day Hour Minute Second Latitude hemisphere Latitude position Longitude

P O

hemisphere Longitude position

2 2 2 2 2 2

Last two digits of UTC year UTC month, "01".."12" UTC day of month, "01".."31" UTC hour, "00".."23" UTC minute, "00".."59" UTC second, "00".."59"

1

'N' or 'S'

7 1 8

S

ddmmmmm,

with

an

implied decimal after the 4th digit 'E' or 'W' WGS84

dddmmmmm

with

an

implied decimal after the 5th digit 'D' if current 2D differential GPS position

I

'D' if current 3D differential GPS

T I

WGS84

Position status

1

O

position 'g' if current 2D GPS position 'G' if current 3D GPS position

N

'S'

if

simulated

position

'_' if invalid position Horizontal posn error Altitude sign Altitude

3

EPH in meters

1

'+' Or '-' Height above or below mean sea

5

level in meters

East/West velocity

1

direction East/West V

velocity

E L

magnitude North/South

O

velocity

C I

direction North/South

T

velocity

Y

magnitude Vertical velocity direction Vertical velocity magnitude Sentence end

4

1

4

1 4 2

'E' or 'W'

Meters

per

second

in

tenths,

in

tenths,

("1234" = 123.4 m/s)

'N' or 'S'

Meters

per

second

("1234" = 123.4 m/s) 'U' (up) or 'D' (down) Meters per second in hundredths, ("1234" = 12.34 m/s) Carriage return, '0x0D', and line feed, '0x0A'

Notes on the table: •

If a numeric value does not fill its entire field width, the field is padded with leading '0's (eg. an altitude of 50 meters above MSL will be output as "+00050").

•

Any or all of the data in the text sentence (except for the sentence start and sentence end fields) may be replaced with underscores to indicate invalid data.

.

GPS Receivers with NMEA Output: Sometimes you would like to place geographical data in your columns Using the Global Positioning System (GPS). This Tech Note will assist

You in setting up columns in your application to accept GPS data entry. Data Plus should work with any GPS unit capable of NMEA output. In configuring the communication settings on your GPS unit, set the Protocol to NMEA and ensure that the “$GPGGA” messages are turned On. Data Entry Tab: 1. Select a file in the Hierarchy on the left side of the screen by clicking On it. That level should now be highlighted. 2. Select the first column that the GPS data will be received. In this Example we are going to use a separate column for the Latitude and For the Longitude. Select the Latitude column by clicking on it. The Column will now be highlighted. 3. Click on the Data Entry tab on the right side of the screen to bring it Forward. 4. Click on the down arrow under User Data Entry Type and choose Serial Port. The Serial Parameters box will appear.

. Input Type: Streaming If a serial device sends its data continually and repeats the Stream of data without a request from the hand-held computer When the transfer is initiated, the Serial Input type is called Streaming. A GPS unit sends a stream of data and repeats a Stream a data at once per second or repeats the data in Whatever interval has been defined. Port: Com 1 This is the Com Port that the GPS unit will use on the handheld. For example, if your hand-held will use Com Port 2, click On this option and change it to Com 2. Baud: 9600, Parity: None, Data Bits: 8, Stop Bits: 1, Flow: None These are settings available for most GPS units. The GPS unit And Data Plus settings must be identical. If you are having

Trouble receiving data; verify that these settings are the same on Your GPS unit. Close On Exit: Checked This option closes the Com port when moving to the next column. This can save power consumption.

Now click on the advanced button In advanced Setups we will set up parameters that will qualify the Sentence to ensure we are getting the GPS position data sentence, Parse the latitude and longitude from the data sentence, and store the Latitude and longitude to the appropriate columns. The following are sample NMEA data sentences from a GPS receiver: $GPGGA,060657,4243.552178,N,11431.147225,W,1,05,2.0,1193.98,M,17.96,M,0000*46

$GPGSA,A,3,19,29,22,18,28,,,,,,,,3.0,2.0,2.2*33 $GPVTG,323,T,,,0.57,N,1.05,K*37 5. Set the Qualifier Type to Word. The Qualifier String is $GPGGA. 6. Use an Offset from Beginning of 0. 7. Set the Parsing Method to Parse NMEA-type. 8. Use a comma for a Parsing Delimiter.

9. Select the Multi Column Store radio button because we want to store The longitude when we store the latitude. 10. In the Multi column store group, Select the Latitude column in the Store In Column drop down. The Latitude is Parse Element Number 2 and Element Number 3 is the North/South reference. Use these as the Element and Cat Element choices. Press the Add button when finished. These settings yield “4243.552178 N” from the example GPS data for the latitude.

These settings yield “4243.552178 N” from the example GPS data for the latitude.

11. In the Multi column store group, Select the Longitude column in the Store In Column drop down. The Longitude is Parse Element Number 4 and Element Number 5 is the East/West reference. Use these as the Element and Cat Element choices. Press the Add button when Finished. This yields “11431.147225 W” from the example GPS data. 12. When completed, press the OK button. This will store the Latitude and Longitude in the appropriate columns from the same reading when the Enter key is pressed. 13. Click on Compile/Save. 14. Click on Test. While the above method does work for collecting the GPS latitude and Longitude values, it should be noted that typical NMEA outputs these Values as always positive and combines degrees and decimal minutes Into one number. The data in this form is not typically of much use to Other data processing programs. To present the data in a more useful form, a custom serial input program can be used to parse through the incoming GPS data strings and convert the values into more meaningful representations in the form of decimal degrees instead of degrees and decimal minutes combined like the NMEA 0183 format. A program such as this is included in the DPCEdit on-line help and may be copied and pasted from the help into a file so that it may

be used with the serial input. The following steps outline how this may be done. First it is advised to adjust the formats of the latitude and longitude columns to numeric, size 13 with a decimal value of 8. Do this by selecting the latitude column, choosing the Data Format tab, then clicking the Edit button and changing the values appropriately. The same should be done with the longitude column.

To present the data in a more useful form, a custom serial input program can be used to parse through the incoming GPS data strings and convert the values into more meaningful representations in the form of decimal degrees instead of degrees and decimal minutes combined like the NMEA 0183 format. A program such as this is included in the DPCEdit on-line help and may be copied and pasted from the help into a file so that it may be used with the serial input. The following steps outline how this may be done. First it is advised to adjust the formats of the latitude and longitude columns to numeric, size 13 with a decimal value of 8. Do this by

selecting the latitude column, choosing the Data Format tab, then clicking the Edit button and changing the values appropriately. The same should be done with the longitude column. To establish the serial input program, follow these steps. 1. Select the latitude column. 2. Click on the Data Entry tab on the right side of the screen to bring it forward. 3. The serial input parameters are assumed to have already been set using the steps above. Click on the Advanced button in the serial parameters box. The advanced serial parameters dialog will appear similar to the following.

4. The Serial Input Program section resides in the lower left portion of the dialog. Click the Edit button. A dialog will appear asking for the name of the program to edit.

5. In the New File Name edit box, type sergps and click the OK button. The DPCEdit program will appear as follows.

6. Since the conversion program already resides in the on-line help of DPCEdit, the help needs to be accessed so the program code can Be copied into the sergps.dpc file that was just created. Press the F1 key to bring up the on-line help. 7. In the help contents, click on the small plus sign (+ ) to the left of

The topic "User Program (DPC) Help Topics." Next, click on the Plus sign to the left of "Sample Programs." Finally, click on "Serial Input." The program will appear on the right side of the display as Follows.

8. From the Edit menu, choose Copy. 9. Close or minimize the on-line help and click within DPCEdit’s sergps.dpc window. 10. From DPCEdit’s Edit menu, choose Paste. The program should Appear in the editing window 11. Press and hold the Ctrl key on the keyboard and press the Home Key in order to move the editing cursor to the very top of the editing Window.

12. Press and hold the Shift key on the keyboard and press the down arrow key four times. The top four lines of the text should be highlighted.

13. Press the Delete key on the keyboard and the four highlighted lines Should be removed. The Sample Program will only allow DGPS positions to be Collected. If you do not have DGPS capabilities, change the <2 to a <1 in the following sentence: if(atof(tstring)<2); 0=old or NO GPS 1=GPS, 2=DGPS This will allow standard GPS positions to be utilized while blocking Old positions. 14. Click on the Tools menu and choose Compile. The program Should be compiled without errors, as shown in the following dialog.

15. Click on the OK button. 16. Close the DPCEdit program. You should now be back in the DataPlus Professional Generator. 17. Within the Serial Input Program portion of the Advanced Serial Parameters dialog, click on the Select button.

. 18. From the file list that appears, highlight the sergps.RUN file and press the OK button.

19. The program should now be selected for use as Post-Parse, as shown.

20. Click the OK button in the Advanced Serial Parameters dialog. 21. Click on Compile/Save. 22. Click on Test.

Smart GPS i-3000 version 7.5: Hardware Specification:

GPS APPLICATIONS

Description of the various applications

Science and research

Commerce and industry

Agriculture and forestry

Communications technology

Tourism / sport

Military

Time measurement